The invention relates to a charging device for charging an electric or hybrid vehicle on an AC power supply system, wherein the charging device has a power supply system plug.
Charging devices for electric vehicles or hybrid vehicles with which a charging connection can be formed between the vehicle and a power supply system are known from the prior art. For example, document CN 202221911 U (D1) discloses such a charging connection which includes a vehicle-side plug (3 in FIG. 1 of D1), a power supply system plug (2 in FIG. 1 of D1) and charging electronics (1 in FIG. 1 of D1).
For the purpose of overheat protection, the charging device is equipped with a temperature sensor which is located in the vehicle-side plug. The temperature sensor ensures thermal monitoring during charging and is intended to avoid overheating, in particular to protect the electrical energy store of the vehicle.
An object of the invention is to provide an improved charging device with thermal monitoring.
This and other objects are achieved by a charging device for charging an electric or hybrid vehicle on an AC power supply system, wherein the charging device comprises a power supply system plug. The power supply system plug comprises a contact pin which is composed essentially of a first material. The charging device comprises a temperature monitor. The temperature monitor comprises two sensor sections which are essentially composed of a second material and which are each connected to the contact pin, wherein the temperature monitor can detect a temperature gradient within the contact pin according to the principle of thermoelectrical potential difference between the first material and the second material.
According to the invention, the charging device includes a temperature monitor, and the power supply system plug includes a contact pin which is composed essentially of a first material, wherein the temperature monitor has two sensor sections which are essentially composed of a second material and which are each connected to the contact pin. The result is that the temperature monitor can detect a temperature gradient within the contact pin according to the principle of the thermoelectric potential difference between the first material and the second material.
It is advantageous here that the temperature monitor can measure a voltage difference which is in direct relationship with a temperature gradient in the contact pin. The two sensor sections are connected to the contact pin. The contact pin has two connecting locations to one sensor section in each case. At each of these two connecting locations, a temperature-dependent contact voltage is formed between the first material and the second material, which second material is different from the first material. Therefore, if a potential (voltage) difference is present between the sensor sections, this means, on the one hand, that given the same configuration of materials different contact voltages are present at the two connecting locations. This is equivalent to a difference in temperature between the connecting locations. According to the principles of the Seebeck effect, i.e. according to the principles of the temperature-dependence of the thermal forces of the thermoelectrical voltage series, an increased voltage means an increased temperature difference between the connecting locations and consequently a temperature gradient within the contact pin.
In this way it can therefore be detected, for example, whether thermal power is generated at the contact location of the contact pin with a contact spring of a socket of the AC power supply system. In such a case, a temperature gradient with a negative gradient is formed originating from the contact location and can be detected with the temperature monitor. It is therefore possible, for example, to reliably detect an increased contact resistance between the contact pin and the contact spring, which contact resistance entails such a temperature gradient in the contact pin. The sensitivity of the temperature monitor is higher the greater the temperature gradient between the connecting locations, i.e. the larger the component of the spatial distance between the connecting locations, which component is directed along the temperature gradient. In other words, in order to detect typical temperature gradients within the contact pin, the connecting locations are selected such that one of the connecting locations is located in a region of the contact pin which is as cold as possible, and the other connecting location is located in a region of the contact pin which is as hot as possible.
According to one embodiment of the invention, the two sensor sections are each connected to the contact pin at one plug-side end of the sensor section.
By means of a direct connection, a temperature gradient which is formed in the contact pin can be detected very quickly. In particular, if the charging connection between the power supply system and the vehicle is subjected to a continuous load with current strengths near to the specification limit of the power supply system plug or of the corresponding socket of the power supply system plug, heating as a result of an increased contact resistance can be detected directly at the source where it is generated.
According to one preferred embodiment of the invention, each of the contact pins is provided with sensor sections. As a result, each of the contact pins can be monitored by the temperature monitor independently of the other contact pin.
Furthermore it is appropriate if the charging device comprises a charging electronics unit. The charging electronics unit is configured to measure and evaluate the thermoelectrical voltage drop between the sensor sections. The two sensor sections are for this purpose each connected to the charging electronics unit at the end of the sensor section lying opposite the plug-side end.
It is therefore possible, for example, for the charging process to be interrupted by the charging electronics unit if the latter measures an excessively high voltage drop between the sensor sections, i.e. an excessively high temperature gradient within the contact pin, or a voltage drop between the sensor sections which changes too quickly, i.e. an excessively high thermal power input in the contact pin. For this purpose, the charging electronics unit repeatedly measures the voltage drop between the sensor sections at a predefineable frequency and evaluates the measured voltage drop according to each measurement result. In this context, “evaluation” means that a temperature difference between the two connecting locations of the contact pin is assigned to the measured voltage drop on the basis of a characteristic diagram which is stored in the charging electronics unit. In the case of an excessively high temperature difference or in the case of a temperature difference which changes too quickly, the charging process can be interrupted by the charging electronics unit or the charging current can be reduced. In this way, damage to the power supply system plug or to the corresponding socket due to overheating is prevented.
According to a further embodiment of the invention, the charging electronics unit comprises a microcontroller. The microcontroller has an analog-to-digital input for the ends of the sensor sections which lie opposite the respective plug-side end, in order to measure a voltage between the sensor sections.
A microcontroller is therefore provided in the charging electronics unit in order to operate the temperature monitor. The microcontroller carries out, in particular, the measurement of the voltage drop between the sensor sections and the evaluation of the measured voltage drop. For this purpose, the voltage drop, which is measured in an analog fashion, is digitized for further data processing.
According to one particularly preferred embodiment, the first material and the second material are respectively two different metals. For example, the contact pin is predominantly composed of iron and the voltage sections of copper. Iron ensures good electrical conductivity between the contact pin and the contact spring. Copper is a suitable conductor for a robust voltage measurement between the sensor sections. According to the thermoelectrical voltage series, metals additionally have a particularly high Seebeck coefficient. The two metals can furthermore be placed directly in contact with one another via an intermetal connection.
For example, the connection of the respective plug-side end of the sensor section to the contact pin can be embodied as a soldered connection between the first metal and the second metal. Alternatively, there can be a welded connection. Both connecting techniques are customary and favorable metal processing methods which have virtually no influence on the Seebeck effect.
According to one particularly preferred embodiment of the invention, the charging device comprises a vehicle plug. For the purpose of charging, the charging device is connected to the vehicle via the vehicle plug and to the power supply system via the power supply system plug. The plugs are connected by a cable which accommodates the electrical lead conductors. The charging electronics unit is integrated into the cable or into one of the two plugs.
The invention is based on the ideas presented below.
It is therefore proposed that a direct metallic connection between the electric vehicle or hybrid vehicle between a suitable thermoelectric voltage metal requires a possibility of charging via the general 230V AC power supply system. For this purpose, charging devices, which permit an electrical energy transfer between the power supply system and the vehicle, are sold for contemporary vehicles. For this purpose, the charging device is connected both to the vehicle and to the power supply system. Therefore, these charging devices are often also referred to as charging cables which have a vehicle-side plug (charging plug) and a power supply system plug for the power supply system.
In order to charge an electric vehicle or hybrid vehicle in an acceptable amount of time, very high charging currents are required which extend close to the specification limit of the sockets of the 230V AC power supply system. Shockproof, plug type F or CEE 7/4 sockets, which are known to a person skilled in the art, are typically used, at least in large parts of Europe for domestic applications, owing to their widespread use. The abovementioned power supply system plug is compatible with one of these socket variants.
A rated voltage of 230V at a rated frequency of 50 Hz is associated with the use of the shockproof plug system. The sockets, the corresponding plugs and the cable lines are generally configured for a brief current strength of 16 A. This corresponds to an electrical power of approximately 3.7 kW. However, only continuous loading with current strengths between 10 A and 12 A is generally permissible. For continuous loading with 16 A over an uninterrupted time period of 6 h, special plug-socket types, such as so-called “camping or caravan connectors,” are permitted. This is stated, for example in the IEC 60309 standard.
The shockproof plug has two contact pins with 4.8 mm diameter, 19 mm length and 19 mm axial spacing for the phase conductor and the neutral conductor. The corresponding socket has contact springs into which the contact pins engage when the plug is plugged into the socket. Owing to wear as a result of plugging in and withdrawing the plug, the electrical contact resistances between the contact pins of the plug and the contact springs of the socket can increase. The contact resistances can also be increased as a result of aging by corrosion, for example by use of the plug system outdoors or in a damp environment. However, incorrect installation or low product quality of the plugs can also cause this effect. An increased contact resistance causes thermal power (Pthermal) to be released at the contact location between the respective contact pin and the contact spring. This effect already occurs at a contact resistance (Rcontact resistance) which is increased by a few 0.1 ohms, according to the question:Pthermal=Imax2·Rcontact resistance,and is approximately 7.2 Watts in the case of a resistance which has increased by 0.5 ohms given a current strength of 12 A. Under continuous load, such a release of heat can result in a thermal event, for example due to melting of the plug which is fabricated from plastics.
It therefore proposed to provide the contact pins with an electronic temperature monitoring system. For this purpose, the charging device is equipped with monitoring electronics, and the contact pins with temperature sensors. Known temperature sensors, such as PTC sensors or NTC sensors, perform a similar purpose, but they are disadvantageous solutions owing to their comparatively high cost and the thermal contact resistance between the contact pin and the sensor.
It is therefore also proposed to produce a direct metallic connection, for example by welding or soldering, between a suitable thermoelectric voltage metal and the contact pins. Depending on the contact pin, two connecting locations, each with a wire section of the thermoelectric voltage metal, are provided for this purpose. Owing to the thermoelectric voltage metal effect, a voltage drop occurs between the two wire sections if a temperature gradient is formed between the two connecting locations in the contact pin. For this reason, the two connecting locations should therefore be provided with the greatest possible spatial distance. As a result, temperature differences within a contact pin can be resolved better in terms of measuring the equipment. For the evaluation of the measurement, a microcontroller is provided in the charging device, which microcontroller has one thermoelectric voltage input per contact pin.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.